1. Field of the Invention
The present invention relates to a stalk switch attached to a steering column or the like of an automobile to operate turn signal lamps or wipers, and more particularly, to a latch mechanism for latching a control lever in an operating position.
2. Description of the Related Art
A left stalk switch and a right stalk switch are usually attached to a steering column of an automobile. One stalk switch is called a "turn signal switch" and used for operating turn signal lamps, and the other stalk switch is used for operating wipers or the like. Of these stalk switches, the turn signal switch rotatably supports a control lever on a housing integrally formed with the steering column. By rotating the control lever from a neutral position to either of left and right turn signal positions, a lamp for turning to the left or the right is flashed, and by rotating the control lever in a direction perpendicular to the turn signal position, beam switching or flashing for passing is performed. In this case, the control lever is latched in the operating position, such as the turn signal position or the beam switching position, and is automatically or manually returned to the neutral position when a steering wheel is rotated in a direction opposite to the indicated direction.
Hitherto, a latch mechanism for a control lever has been widely used in which a driving member is slidably held at the base end of the control lever via a spring, and the driving member is pressed into contact with a cross-sectionally V-shaped cam surface that is provided in the housing. In the conventional latch mechanism, a projection is formed in the middle of an inclined surface of the cam surface. By rotating the control lever from the neutral position to the operating position, the driving member slides from a valley to a peak of the cam surface against an urging force of the spring, and the control lever is latched in the operating position at the time the driving member passes over the projection.
According to the conventional latch mechanism, since the control lever is latched in the operating position by locking the driving member with the projection of the cam surface, the control lever cannot be securely latched unless the urging force of the spring for urging the driving member to the cam surface is set to be large. For this reason, the rigidity of the base end of the control lever must be increased by increasing the thickness thereof, and the rigidity of the housing must be increased by increasing the thickness of the cam surface, whereby the overall size of the stalk switch is increased. In addition, since a spring having a large urging force is used, a large amount of force is required to rotate the control lever, and the length between the rotation support and the terminal end of the control lever is necessarily increased, whereby the size of the stalk switch is also increased.